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Virtual endoscopy improves the effectiveness of lung biopsies

Virtual Navigator converts a patient’s CT scans into a 3-D representation of the lung.

Melissa Beattie-Moss

January 26, 2009

Virtual endoscopy improves the effectiveness of lung biopsies

When lung cancer is suspected in a patient, physicians typically rely on imaging tests such as chest x-rays and computed tomography (CT) scans to diagnose and stage the disease. Obtaining a complete and accurate diagnostic picture is vital, since treatment decisions depend on information about a tumor’s size, type, location, stage, and aggressiveness. Often, minimally-invasive biopsies are performed to extract a sample of the suspicious lung lesion for analysis, by inserting a long, lighted tube (a bronchoscope, or in broader terms, an endoscope) into the patient’s airways to excise a small tissue sample.

William Higgins

Matching endoscopic views in the lower lobe of a patient's left lung. The thin blue line represents the endoscope's path, starting from the trachea. In the virtual image (right), the blue arrow designates the optimal biopsy site. In the live video view (left), the silver tip at upper right is the biopsy needle.

Explains Higgins, physicians are hamstrung by inefficient work tools. “They have the single CT scan up on the screen, but it doesn’t correspond to what they’re looking at through the bronchoscope,” he says. “One is a 2D video through the airways and the other is flat.” In order to check their position in advance of a biopsy, they have to verify their position with fluoroscopy, increasing x-ray exposure. While alternating between the three images as a guide, the bronchoscopist must advance the instrument via the trachea into the complex maze of airways in search of the suspicious mass. “They can get the lymph nodes pretty well,” says Higgins, “but tumors deep in the airways are hard to get to.”

Much depends on the bronchoscopist’s skill—“which varies greatly,” he notes—especially when biopsy sites are beyond the airway walls. In those cases, finding the right spot to insert the bronchoscope’s needle for a tissue sample can be “hit or miss,” Higgins adds. If the bronchoscopists lose their anatomic orientation during the procedure, they must pull the endoscope back through the airways to a recognizable landmark such as the main bifurcation (branching point) of the trachea and try again.

Each successively smaller bifurcation of the airway tree—called a “generation” and assigned a number—becomes more difficult to navigate. Notes Higgins, “Studies at Penn State Hershey Medical Center have shown that by generation three, bronchoscopists are down to a 50 to 60 percent success rate. At generation four, it’s down to about 30 percent. It’s abysmal. They’re just lost.”

Higgins and his research group, including Hershey Medical Center pulmonologist Rebecca Bascom, are hoping to show them the way. Funded by the National Institutes of Health, the National Science Foundation, and the Whitaker Foundation, the team has developed and tested an interactive software program for 3D image processing and visualization called Virtual Navigator. Designed to interface with standard videobronchoscopy equipment, the software converts each patient’s CT scans into a virtual three-dimensional construction of their particular lung anatomy.

The system then uses techniques from computer graphics and computer vision to generate a detailed ‘procedure plan’—essentially a road map to particular tumors and nodules—prior to the bronchoscopy. “The computer procedure plan is directly linked to the bronchoscope procedure, through a live registration and fusion of the 3D CT data and bronchoscopic video,” Higgins explains. While performing the procedure, the doctor and technicians coordinate their surgical instruments with three-dimensional CT images as they explore the lungs by direct view through their endoscopes. This new approach provides physicians with significantly improved visual feedback and quantitative distance measures to help them decide how to maneuver the bronchoscope and where to insert the biopsy needle.

“Virtual endoscopy permits a level of precision and safety never before achieved in biopsying suspicious lung lesions and staging lung tumors,” says Higgins, who founded a company called Endographics Image Systems, Inc. in 2000 and has made applications to the U.S. Patent and Trademark Office.

Most importantly, says Higgins, initial results from trials led by Bascom at Hershey indicate that the variation in skill level between different physicians is greatly reduced by the system, and biopsy effectiveness is increased.

William Higgins, Ph.D., is distinguished professor of electrical engineering in the College of Engineering, weh2@psu.edu. Rebecca Bascom, M.D., is professor of medicine in the College of Medicine.